A variety of applications could benefit from a material or device having a stiffness that can change from a first (flexible) state, in which the material is shape-formable to a desired shape, to a second (more rigid) state, in which the desired shape can be held or fixed.
Some existing shape-formable devices employ discrete particles (i.e., bulk media) in a gas impermeable envelope that normally move freely with respect to one another, but “jam” together and resist relative motion when the internal pressure of the envelope is reduced below ambient pressure. This jamming of bulk media has been proposed for a variety of products, from a medical restraint for babies (U.S. Pat. No. 4,885,811) to limb demobilization (U.S. Pat. No. 4,657,003), to the stabilization of patients during surgery (U.S. Pat. No. 6,308,353), to robotic end effectors (U.S. Publication No. 2010/0054903). One significant disadvantage of bulk media jamming is the significant volume required for a bulk media-filled device. The bulk media does not lend itself well to thin, sheet-like, applications.
Other existing devices or systems employ bending stiffness variation in a thin form factor. By putting sheets of material in an envelope and removing air from the envelope (e.g., as in U.S. Publication No. 2012/0310126 and Ou et al., “jamSheets: Thin Interfaces with Tunable Stiffness Enabled by Layer Jamming,” TEI '14 Proceedings of the 8th International Conference on Tangible, Embedded and Embodied Interaction, pages 65-72, Association for Computing Machinery (ACM), February 2014), a relatively thin article can be achieved with a variable bending stiffness. They achieve a low bending stiffness in an unjammed state, despite having a high Young's Modulus (or tensile modulus), by allowing multiple thin layers of material to slide over each other. However, because these individual layers each have a high overall Young's Modulus, even in an unjammed state, and they are substantially continuous in one or more axes within the plane, they cannot be easily extended within the plane, or major surface, of the thin article. Because the individual layers lack this extensibility, the conformability of the layers is also limited. Thus, these layers can only take on complex shapes by generating wrinkles, and not by smoothly and continuously assuming arbitrary shapes. The bending stiffness of these systems can increase under vacuum, because the multiple layers jam together and behave more like a single thick layer of the high Young's Modulus material.